Strong acids such as hydrochloric and sulfuric are commonly used in many industrial processes in which during use various metal ions are picked up by the acid. In subsequent use or recycling to the process the presence of such metal ions is undesirable and it becomes necessary to remove these ions from the acid solution. While it is possible to do this in dilute acid systems, it is much more difficult to precipitate the metal ions from strong acids, eg. &gt;2M.
In a particular application, 28% HCl is employed in the acidizing of oil wells. To improve the efficacy of the acid treatment surfactants are frequently added to the acidizing solution. If there is too much iron in the system, the surfactants have the tendency to form a separate phase. In order to overcome this tendency, the concentration of iron must be reduced or it must be removed completely.
Aluminum is another metal which can cause problems in certain processes and it, too, must be removed. In a particular application both iron and aluminum are dissolved by 25% sulfuric acid which interferes with the process in which the acid is used. These ions, therefore, must be removed before recycling the acid to the process.
While certain metals, eg. lanthanum, have been complexed with some aminophosphonic acids, eg. nitrilotri(methylenephosponic acid) (NTMP) and precipitated from dilute acid solutions, the precipitate dissolves in stronger acid solutions (see Chem. Abst. 102(18): 159728Q). In another reference (Anal. Chem. vol. 39, no. 8, 1967, pp 998-1000.) ferric iron was precipitated in acid solution with NTMP at a pH of 2.5, but was redissolved at pH of &gt;4. The use of NTMP to precipitate aluminum is accomplished in 0.1M HCl, in combination with diethylenetriaminepentaacetic acid to prevent the co-precipitation of transition metals. This is reported in Chem. Abst. 84:83673e. Another study, reported in Chem. Abst. 101:178453s, covers the solubility of the aluminum subgroup of metals with certain organophosphorous complexing agents, including NTMP and ethylenediaminetetra(methylenephosphonic acid) (EDTMP) in solutions of H.sub.2 SO.sub.4 of up to 0.25M. The precipitation of Indium from 0.1M H.sub.2 SO.sub.4 by using p-hydroxybenzyl-amine-N,N-bis(methylenephosphonic acid) is disclosed in Chem Abst. 100:195666.
It has now been found that certain organic aminophosphonic acid compounds will cause iron and aluminum to precipitate from acid solutions of &gt;2M.